In recent years, display devices having a touch panel function of a capacitive type, which can be operated intuitively and which is capable of multi-point detection, have been drawing public attention. However, with such a display device, the thickness of the display device increases by the thickness of the touch panel substrate, and the display quality will be lowered because of a decrease in transmittance due to the touch panel substrate. Moreover, the terminal provision area of the touch panel substrate is separate from that of the display device, thereby making connections difficult.
As a mode to solve these problems, in-cell-type touch panels have been under discussion, in which the touch sensor function is incorporated into the liquid crystal display device itself. This is to address problems, such as the provision of touch sensor electrodes inside the liquid crystal display device, which complicates the display device manufacturing process, the touch sensor electrodes affecting the display quality, the inability to increase the driving frequency, thereby limiting the realization of large-size products.
Patent Document No. 1 discloses a liquid crystal display device, in which the common electrode is utilized also as a driving electrode of the touch sensor, and the detection electrode is formed on the opposite side of the counter substrate from the liquid crystal layer. While the common driving signal applied to the common electrode is to determine the display voltage of each pixel together with the pixel voltage applied to the pixel electrode, it serves also as the driving signal for the touch sensor.